Graphite is a good solid lubricating material. It is known that a powder metallurgy product by plating copper or sliver on graphite particles will have a good property for abrasion resistance and self-lubrication.
U.S. Pat. No. 4,240,830 disclosed a process (hereinafter called as xe2x80x9cprior processxe2x80x9d) for plating copper or silver on graphite particles as small as 38 microns. In this prior process, the preparation of the graphite powders includes heat treatment in a hydrogen atmosphere up to 1000xc2x0 C., and the graphite powder is then sensitized in a stannous-stannic chloride solution and when copper plating is undertaken, activation by contact with a silver nitrate solution is carried out. The prior process is complicated with high production cost, and should be subjected to hydrogen atmosphere at high temperature. Hydrogen has an ignition temperature of 1085xc2x0 F. (585xc2x0 C.) and a flammable limit of 4.0xcx9c75% by volume in air. So, it should be very careful to treat the dangerous and easily explosive hydrogen under high temperature, thereby requiring strictly controlled working environment, process equipments, and operation management and possibly increasing the production cost.
The present inventor has found the drawbacks of the prior process for plating copper on graphite particles, and invented a process and apparatus for plating copper on particulate graphite safely and economically.
The object of the present invention is to provide a process for plating copper on particulate graphite comprising the steps of:
1. Cleaning and drying the graphite particles;
2. Preparing a plating solution including aqueous solution of cupric sulfate and glacial acetic acid; and agitating the plating solution with the graphite particles as cleaned for circumferentially wetting the aqueous solution of cupric sulfate on the graphite particles;
3. Dripping the graphite particles as wetted with a layer of the aqueous solution of cupric sulfate on a rotating metal (including zinc, aluminum and iron) disk to conduct a displacement reaction within the layer of the cupric sulfate solution to plate copper, as displaced by the metal existing in situ on the metal disk, on each graphite particle; and
4. Washing the graphite particles as plated by copper with water and then drying the copper-plated graphite particles.
Another object of the present invention is to provide an apparatus for plating copper on the graphite particles with a safe and economic process.